STAUEASTRUM. 131 



Cells minute, a little longer than broad, verv sliofhtlv 



' ' il O / 



constricted, sinus very obtuse-angled (about 140) ; 

 semicells quadrate-cuneiform, sides almost straight, 

 apex concave, apical angles a little produced and 

 rounded. Vertical view tetragonal or pentagonal 

 (more rarely trigonal), with concave sides and rounded 

 angles. Cell-wall smooth. 



Zygospore unknown. 



Length 8-12 p.; breadth 7-9 p,; breadth of isthmus 

 6-7'5/x. 



Geogr. Distribution.- -Germany. 



The above description and the measurements refer to 

 St. minutissimum as described by Reinsch, and fig\ 2 on 

 PL CXIX is a copy of one of Reinsch's original figures. 



So many different forms have been referred to " Staurastrum 

 minutissimum Auersw." that it wasfelt to be an absolute neces- 

 sity to carefully examine Auerswald's original specimens. 

 Fortunately, these were issued in Rabenh. Alg. Europ. 1863, no. 

 1428 (c. fig.)- All the specimens thus distributed consist of a 

 stout form of St. inconspicuum Nordst., and both the descrip- 

 tion and figure given by Auerswald are erroneous. Therefore, 

 the only ( St. minutissimum ' which can be regarded as a 

 valid species is that described and figured by Reiusch in 

 1867, and hence Reinsch must remain the authority for this 

 species. Even then the species remains doubtful, as nearly 

 all the published figures since 1867 differ widely from those 

 of Reinsch. 



Most of Reinsch ; s figures represent a minute Staurastrum 

 with concave apices, and this we have regarded as the type- 

 form. We suo-p-est the following arrangement of the other 



o O O o 



known forms of St. minutissimum : 



Var. CONVEXUH nob. [= St. minutissimum Reinsch, Spec. 

 Gen. Alg. 1867, t. 23 A II, f. 1, 2.] Constriction of cells 

 somewhat deeper ; apex of semicells convex. (PI. CXIX, 



Forma trigona. St. minntissimum forma tngona major 

 et minor Wille, Ferskv. Alo\ Nov. Semlj. 1879, p. 52, 

 t. 13, f. 59, 60; Larsen, Freshw. Alg. E. Greenland, 1904, 

 p. 98. Vertical view triangular, with very slightly con- 

 cave sides. Length 18-29,u; breadth 17-29 /u; breadth 

 of isthmus 9-11 /u. (PL CXIX, fig. 5.) Halt. Green- 

 land. Nova Zembla. 



Forma tetragona. St. minutissimum forma tetragona 



